Various materials are used for air filter media. One common material is non-woven polyester batting, a high loft material that provides an effective filter, while being relatively inexpensive to manufacture. Fibreglass is another material that is commonly used for air filter media. However, there has been a shift to using polyester and other synthetics as filter media, which have improved filtering and dirt-trapping properties.
A common air filter assembly has a cut-out sheet of filter media encased in a rigid cardboard, plastic or metal frame. The frame is used to support the filter media and to keep it fully planar and to prevent the lightweight media from being blown through the air passageway or duct. In many cases, the air filter assembly must be kept in an upright position, so the material must also be supported against sagging. The media itself has almost no body. The frame is also used to protect the filter media, particularly the edges of the media sheet, to prevent fraying and fibre loss. The frame is open in the center, acting as a channel allowing air to pass through the filter media.
In many cases, air filters are considered a consumable item, and manufacturers are under pressure to keep costs down without losing filter effectiveness. As a result, unless there is a structural need to have the filter encased in a metal or plastic frame, cardboard is often preferred as a much cheaper alternative. The cardboard frame can be folded from a paperboard blank. Various methods for making a cardboard frame with finished corners from a paperboard blank, with and without adhesive, are known.
However, there is still a cost associated with the cardboard frame. In addition to the cost of the materials, there is a cost associated with the assembly of the air filter within the frame. Furthermore, there is an environmental cost associated with disposal of the entire filter assembly.
It would be desirable to provide an alternative to the traditional air filter assembly.